A technique for cooling hot members, such as a rotor blade, a rotor disk, or a stationary blade in a gas turbine, by using steam instead of air as a cooling medium, is now being used, in order to increase the thermal efficiency in the gas turbine. This is due to the following reasons. The specific heat at constant pressure of dry steam is cp=1.86 kJ/kgK under a normal condition, which is a value almost twice as large as the specific heat at constant pressure of air, cp=1.00 kJ/kgK. Therefore, steam has a large heat capacity and a high endothermic effect, as compared with air of the same mass. Further, when wet steam is used as the cooling medium, the endothermic effect can be further increased, since the latent heat of vaporization for the wet amount can be also used for cooling. Hence, the cooling efficiency can be increased than when using air, and the turbine inlet temperature of the combustion gas can be increased, thereby enabling an improvement in the thermal efficiency.
In the conventional air cooling, air from a compressor is used as a cooling medium for rotor and stationary blades of the turbine. However, when this compressed air is used for cooling, the work that can be taken out from the turbine decreases. If steam is used instead of air, the cooling air for the rotor and stationary blades can be saved, and hence the work that can be recovered by the turbine increases by this amount, thereby the work that can be taken out from the turbine can be increased.
FIG. 15 shows a rotor disk in a gas turbine conventionally used. A plurality of first stage rotor disks 500a to 500d are fastened by a spindle bolt 520 and nuts 510, to thereby constitute a rotor 600 of a gas turbine. Spaces between the rotor disks 550, 551 and 552 become a path for flowing steam supplied to the rotor blade (not shown), and cooling steam is supplied from a hollow turbine main spindle 560 side. This steam flows through the path formed by the spaces 550 and 551, and is supplied to the rotor blade from the space between the first stage rotor disk 500a and the second stage rotor disk 500b. 
However, since the steam pressure on the rotor disk side is higher than the air pressure on a compressor side, the steam on the rotor disk 500a side leaks towards the compressor side, through a bolt hole provided in the first stage rotor disk 500a. The amount of leakage is not large as seen from the whole feed rate of the steam, but recently, it is tried to suppress the steam leakage, even in a small amount, and to use the cooling steam as effectively as possible. Therefore, it is necessary to reduce the steam leakage in this part as much as possible.
It is therefore an object of the present invention to provide a gas turbine that can reduce the leakage of steam to be used for cooling the rotor blade and the like and increase the use efficiency of the steam, thereby enabling efficient operation, and a sealing structure of the spindle bolt for connecting the rotor disks.